In prior art the surroundings of a vehicle is captured with a camera mounted on the vehicle to display captured images on a monitor in a vehicle cabin, thereby assisting a driver and a passenger to pay attention to a blind spot from their view.
Furthermore, there is a technique in which images captured by the camera are processed to automatically detect a moving object in the images and attract a passenger's attention when the moving object is approaching the vehicle.
For detecting a moving object approaching a self-vehicle, for example, there is a known method in which continuous images in time series are subjected to optical flow processing to detect from the images a region (an image portion) whose position is changed as a moving object (Patent Documents 1 and 2).
Another technique has been proposed in which a region corresponding to moving object is identified from the images to find an enlargement rate based on a change in distance between the vertical edges of the identified region corresponding to the moving object and determine whether the moving object is approaching according to the enlargement rate (Patent Document 3).